Yes, she is. And if she isn't, she eventually will be. Resistance Is Futile. Narrative Causality compels you.
A standard response in the face of an accusation that two characters are more than Just Friends. Usually said with an exclamation point - or ten - at the end, and emphasis on the "NOT", maybe accompanied by breaking something.
"He is not my boyfriend!" is another version, albeit not as common, probably in a 65/35% ratio. There are also instances when the two accused say it simultaneously.
Is it true? Technically, yes. Hilarity, if not bloodshed, ensues, because:
A common inversion, especially in the second case, is when the speaker is asked about the not girlfriend/boyfriend in question, and they respond with the line, even though the accusation was never brought up in the first place. Alternately, the accusation is made, but not the name, which the defendant then gives up. In either case, cue satisfied smirk by the asker.
The amount of exclamation marks and how much the characters protest and try to convince people that they aren't together is usually proportionate to the amount of Unresolved Sexual Tension between the characters in question. Presumably characters who really aren't wouldn't feel threaten by the accusation.
Especially common in shows and on channels ("Teen" Nick goes crazy with this) where kids and/or preteens are the main audience. Quite interesting, as more often than not, most kids aren't ready for that kinda stuff yet, and therefore could use whatever interpretation comes their way. For some, the trope can be coupled with the fact that it allows for both a male and female protagonist in starring roles (thus reaching a wider audience) but is as far as the either the Media Watch Dogs or writers will ever go in terms of illustrating romance and relationships in a series.
See also Relative Error, for when the pair involved are relatives of each other, and Mistaken For Romance.
One of the stock phrases for Tsunderes (both genders), or one/both of a couple who are Just Friends.
This does not result inThe Not-Love Interest.
Compare/contrast with Stupid Sexy Friend, wherein deciding they should just be friends is contrasted with the thoughts of being more than friends one can't get rid of.
Lucy has to deal with this trope a number of times. People have mistakenly hooked her up with Natsu, Gray, Loki/Leo, and Ren from Blue Pegasus.
This occurs with Elfman and Evergreen as well during the S-Class Trial Arc.
When they were younger, Gray would constantly follow Erza around and challenge her to fights. His peers teased him for this and asked if the real reason was because he was in love with her. He got embarrassed and denied it.
Edward Elric says this frequently about Winry Rockbell. When Ed calls Winry to get his automail repaired after a run-in with the homunculi and Brosh asks him if he's calling his girlfriend. Ed gets so incensed by this proposition that his yelling reopens his wounds. Later Ed has a spectacular Spit Take at Hawkeye's suggestion that he loves Winry nearly drowns poor Hayate. It also happens in the 2003 anime after Edward passes the state alchemy exam and writes to Winry to tell her so, Nina says that "Winry is a pretty name" and asks if she is his girlfriend, at which point, he flips out to a comparable degree of his height Berserk Button.
Winry insists to Rose that Ed is her childhood friend, despite the fact that she has already admitted to herself that she is in love with him.
It has Inuyasha calling Kagome "shard detector" in early chapters/episodes to deny any relationship with the reincarnation of his old girlfriend. She resents it every time, at first because she's a person, not just a detector, and later because of the Belligerent Sexual Tension between them. The most famous instance of this is probably Miroku's entry episode (episode 16, "Mystical Hand of the Amorous Monk, Miroku!") near the end, where he denies a relationship... with Luminescent Blush and stuttering.
Even before that Inuyasha has the famous We're NOT lovers exchange with Kagome in the Thunder brothers arc.
Kagome also has several He is not my Boyfriend moments including one where her friends ask her about her boyfriend and she replies that they are not together and were thrown together by a cruel twist of fate. This confuses them greatly as they were referring to Houjo.
Most of the romantic comedy in .hack//Legend of the Twilight revolves around Shugo's and Rena's attraction to each other — and their efforts to deny it — in the first half of the series (they stop being embarrassed about in the second half).
A similar version is executed in RahXephon with Ayato and Meg, the Shinji-Asuka equivalents of the show, down to the simultaneous blushing shout. In this case however, their statement is true: Meg does have a crush on Ayato but he's interested in Haruka.
The title character from Nadia: The Secret of Blue Water obviously has feelings for Jean, but she declares otherwise to both Grandis and Marie when both call her out about it. (Naturally, since she has never known anything about love before, she does not know how to acknowledge it or express herself.)
A large portion of their fellow students assume that Haruhi and Kyon are dating; Kyon's friend Taniguchi in particular is completely convinced of this, no matter how often Kyon says otherwise. Also, after Kyon and Nagato finally defeat Ryoko the Girl with Psycho Weapon, Taniguchi finds Yuki lying against Kyon while holding onto his arms, and now Taniguchi firmly believes that Kyon had sex with Yuki in the classroom... Kyon's heated (for him) over-explanation doesn't help. His friend points out that for both KyonandYuki to show that much emotion over anything is very suspicious. Which is absolutely correct.
After Haruhi and Yuki, there is an inverted case in the 7th novel with Mikuru and Kyon. Kyon is asked if Mikuru is his girlfriend by some (apparently) random guy. Kyon actually replies that she is his girlfriend, to make the situation not any more awkward.
Kyon seems to have a knack for this trope. The 9th novel mentions that people apparently thought his strange friendship with Sasaki meant that she was his girlfriend.
Chiaki from Nodame Cantabile keeps denying vehemently that Nodame is his girlfriend — even though he spends massive amounts of time with her, mostly at his own place. Things don't get any clearer when he decides to bring her to see his father, which does lead to a temporary break-up though.
Not to mention hugging her a few times, kissing her a couple of times, asking her to come to Paris with him, letting her stay in his room when he's not around, letting her share a bed with him... the man is stubborn.
Souichi from The Tyrant Falls in Love reacts violently when, after having sex, Morinaga suggests that they are "lovers" and later on, "sex friends" (his response to the latter is punctuated by dumping hot coffee on Morinaga's head). All this leaves poor Morinaga wondering just what kind of relationship they do have.
The anime did this a few times with Ash being mistaken for being Misty's boyfriend, especially in the second movie.
One rather serious time was when James and Jesse sprung their trap on the two (while they were riding on a blimp), but then, realizing Brock wasn't there, mistook them for lovebirds on a date. Of course, they both vehemently denied it and got angry... And then everyone realized no-one was piloting the blimp. It didn't end well.
Misty was also asked if Tracey was her boyfriend. Naturally, she denied it.
Also, Drew and May invoked this trope as well, when Harley directly asked them if they were dating.
And in one episode, a couple accused Ash and May of being a couple.
Pokémon Special toys with this in the Emerald arc. We may never know if Ruby actually forgot, refuses to admit his feelings in public, or secretly likes the reaction, but his feigned amnesia in regards to his confession to Sapphire at the end of the R/S arc drives Sapphire up a wall so goddamn hard.
Makoto and Sekai in School Days do this constantly, even after they start sleeping together.
Rina Touin from Mermaid Melody Pichi Pichi Pitch starts out saying this about Masahiro Hamasaki, especially in the manga (his anime incarnation gets off a little lighter, mostly because he's introduced at about the same time as Nagisa and he and Hanon need all the help they can get).
Ranma ˝: Ranma and Akane repeatedly deny that they share romantic interest. In fact, whenever someone mentions them being engaged, they immediately try to explain that it was their parents' choice, not their own choice. Sometimes, however, when some other man is after Akane, Ranma doesn't deny it. He actually brings it up and says that she's his fiancée. It's one of his Crazy Jealous Guy habits.
In one of the first arcs, Konohamaru asks Naruto if Sakura is his girlfriend, and Naruto says yes. Sakura was so furious she punched him.
At a time when Naruto and Sakura are on a date, someone says to Naruto, "Treating your girl?" To which he responds in embarrasment: "No, it's not like that."
Similarly, in a flashback, Sai asks Naruto if he likes Sakura, and he gives a typical reaction. He then responds to Sai's question of if she knows how he feels that he can't tell her how he feels as long as he hasn't kept his promise to bring Sasuke back.
Edo! Minato - as in, Naruto's zombie dad - decides to ask if Naruto and Sakura are together in the middle of a war. Naruto replies "Sort of". Sakura gets angrily embarrassed and responds with violence once again.
Minato: ... Are you Naruto's girlfriend?
Naruto: Uh ... um, yeah! Well, that's more or less it ...
Another variation: Japan had sex with his close friend Greece (more exactly, Greece learns that Japan's sex life is rather "non active" and gives him a "private lesson" to help him) and is in denial about that too. "It was just a dream!A dream! A DREAAAAAAM!"
And in another strip, while holding a practice conversation in Japanese with Greece, Greece asks him who "Nekojiro" [aka the pretend name Japan assumes for himself in that conversation] gets along with. Japan replies, "His friend, Nekokichi-san." Greece smiles and asks if he's "Nekokichi-san", which causes Japan to blush and stammer for a bit before replying with "No comment." Take from that what you will.
And England gets it played straight in a certain drama CD when France calls an Anglo-American argument everyone was eavesdropping on a "lover's spat" which he of course denies.
Bakugan Battle Brawlers gets a few of these. Dan and Runo have the majority of these, more commonly in season 1, but Julie recently gave the "He is not my boyfriend!" line regarding Billy. This prompted a response of, "Now she's breaking up with me!" from Billy, who had an obvious crush on Julie from the very beginning. This was all of about a minute before things changed.
Averted in the manga. After Rukia's habit of dragging Ichigo off to hunt hollows starts rumours flying around the school (actually, Keigo starts them to cause trouble but Ichigo never finds this out), the girls end up asking Rukia (to her Spit Take surprise) if there's anything going on and Rukia confirms there isn't. That is the end of it and this trope never comes into play. Word of God confirmed he wasn't interested in writing a romance story and views Ichigo and Rukia's relationship as more than friendship but less than romance.
This trope is played straight in the anime, however, as the animators rewrote this scene to include rainbows and turn it into a Just Friends scene complete with all the romantic undercurrent this trope evokes. The animators have written this trope for Ichigo and Rukia into the anime on as many occasions as they can get away with, usually in filler scenes where they will use filler characters in an Everyone Can See It manner or even rewrite canon characters (such as Nel) in a Clingy Jealous Girl way to imply there's something going on between Ichigo and Rukia. None of it is based on anything from the manga, however.
In "Memories of Nobody", Ichigo is forced to buy Senna a new ribbon after she accidentally steals one. The shopper keeper asks if it's a present for his girlfriend, triggering this trope.
Camie the mermaid in One Piece does a variation of this trope when asked if she was Hachi's girlfriend, and her blushing and nervous reply neatly confirms her love for him, which had been strongly implied ever since his cover arc.
Taiga and Ryuji of Toradora! are a shining example of this. Taiga goes on a massive parade of destruction upon finding out that the whole class was gossiping about them. It doesn't help that Taiga hangs out at Ryuji's house and he makes her Bentou every day, and they go to and from school together and they eat dinner together just about every day.
Note that at that point it's actually true — they eventually do get together, at which point the rumors have pretty much run its course because it's fairly obvious to all onlookers.
Nagisa and Tomoya from CLANNAD anime, before they went on and became the Official Couple. And even then, the denial is relatively minimal. When directly confronted with the accusation that she and Tomoya might be dating, Nagisa hastily looks away with a nervous blush and replies with what basically boils down to, "May we talk about something else, please?" In the Visual Novel, Nagisa and Tomoya are more open about their relationship, although Tomoya still tries to hide it from Sunohara out of embarrassment (it doesn't work).
Fudo Yusei of Yu-Gi-Oh! 5Ds pulls this off after Aki's dad gets Yusei to help Aki after her duel with Misty. Martha jokes Yusei for crushing on Aki — a fact that Yusei vehemently denies.
Was used before in Duel Monsters, when Mai saw Yugi and Téa hanging out (before the Battle City is announced) and asks if they are dating (technically they kind of were on a date, but Téa still points vehemently that they're just friends).
Happens early in Yu-Gi-Oh! ARC-V to Yuya and Yuzu. Sora asks Yuzu to get Yuya to mentor him, saying he'd do it if his "girlfriend" asked him to. They both deny it(with Yuzu in particular blushing), but Yuya goes a step further by saying he wouldn't be with a "rude girl" like her. Cue paper fan smack from Yuzu.
Said by Kousaka from Genshiken, in his usual flippant way. His "not girlfriend" tries to change this any way she can, with little success. This doesn't last very long (all of three chapters, in fact), as the Genre Savvy Genshiken tell him to just admit it. He does, and thereafter goes from denying it to just not making a big deal out of it.
Gunslinger Girl. Said by Triela to Maria Machiavelli, when the latter hints that Triela is in love with her handler Hillshire. The usual awkwardness is absent as Triela makes it clear that even if she was in love, the fratello relationship doesn't work that way. At least it's not supposed to.
A variation of this is found in Full Metal Panic! with Sōsuke about Kaname. During a dance party on the Tuatha De Dannan, Kurz mentions to Sōsuke that Kaname is very pretty, cute, and has a nice sense of style. Any man would fall for her in an instant. Sōsuke coldly and cuttingly replies that he wouldn't know, since he isn't interested. This is very interesting, considering that this might be one of the few instances where Sōsuke acts like a Tsundere (breaking from his usual stoic manner).
Yuko from xxxHOLiC displays this kind of attitude in relation to her not-boyfriend Clow, and she tends to get rather vindictive should someone suggest she had some kind of relationship with the guy.
Trigun. When a couple bodyguards assume she's fighting with her "boyfriend", the Broom Boy (a.k.a. Vash the Stampede), Meryl Stryfe is very quick to inform them that not only is he not her boyfriend, but she doesn't even like him! Whatever she has to tell herself to get through the job.
In Bakuman。, Fukuda volunteers to help Aoki with her manga illustrations, but is keen to make it clear to his editor, who asks why he is helping a rival mangaka, that he has no interest her. It ultimately turns out that he really doesn't have any apparent feelings for her, since she ends up with Hiramaru without him being at all displeased about it, and it proves his commitment to "Team Fukuda" changing Jump.
Fukuda: And just for the record, I don't have feelings for her or anything. I actually kind of hate her. Yujiro: You don't act like you hate her.
Miu: He's not my boyfriend! He's more like a little brother, or even a dog, you know like a stray dog you bring home because you feel sorry for it? Kasara: Hey, aren't you taking that a little too far?
Spelled out by Kyousuke regarding Manami in episode 6. His friend Akagi calls him out on the seeming hypocrisy of his explanation.
Akagi: So basically she's nothing more than a childhood friend to you, you're not going out with her, you have no feelings for her, but you won't allow other guys to make a move on her? Kyousuke: Yeah, so? Akagi:[sighs]
The original novel, however, goes on with this Platonic Life Partners-ish excuse he makes to the reader when he feels his phrase sounded like he was in denial:
Well, the answer was my honest. I just don't think there is a sharp-eyed guy that could see the appeal behind Manami's homeliness, but if he does appear, I'm going to defend her with all I have. Got it? It's in her company I can relax the most, even with nothing romantic about that. I won't give in to anyone who'd try and take that away from me.
In Lucky Star Most of the times Misao asks Kagami about Konata.
Kanami:[grinning]Is it, by any chance, that you don't want to follow Contractors, but a certain man? Misaki:[turning to her, frowning, blushing, sweating and screaming] Wha— That's not... Kanami:[cheerful] Oh, I knew it! Your dear BK-201. Your panicking confirmation.
Spice and Wolf has several instances of Lawrence calmly explaining to others that he and Holo aren't in that sort of relationship. At some point along the way, it starts becoming something of a lie.
In Durarara!! people generally assume that Mikado and Anri are dating. When they explain that they aren't, the typical reaction is usually, "Really?... Sweet, I have a shot at her, then!" Note: They do not.
Aoba also says this to his Blue Square members regarding Mairu and Kururi. Turns out it's rather tough to explain away that they both kissed him.
Aria and Kinji of Hidan no Aria say that about each other several times.
Fujimura from Fujimura-kun Mates insists that he and Eri are just friends. But he never completely rejects her constant advances.
Mobile Suit Gundam 00 features a rather hilarious subversion in it's second season when Mileina asks Setsuna and Marina if they are a couple. Both reply negative in complete deadpan (and in perfect sync) without a hint of embarrassment or sexual tension.
In the ending of Muhyo And Roji, Busujima tells Imai that her "boyfriend" Roji got back together with Muhyo despite failing the advancement test, prompting her to get angry at the use of the term.
In Martian Successor Nadesico, Akito repeatedly denies that Yurika is his girlfriend or that he's even interested in her. She refuses to believe that however, much to his chagrin.
Shouma and Ringo from Mawaru-Penguindrum go through several rounds of saying this about the other.
Kyo gets pissed when any of his family teasingly suggests that he has a crush on Tohru. It's turned on its head at the end of the series, when some classmates notice the two being clingy to each other. When they ask as a joke if the two are now dating, Kyo matter-of-factly states that yes, they are.
A rather funny variant happens at one point, when a girl tries to confess her love for Kyo, only for him to brush him off. Uotani makes a snarky comment, leading to the girl somehow concluding that Uotani is the girl he's in love with. Since they don't exactly get along, they don't take to this theory well.
DO YOU HAVE KNOTHOLES FOR EYES???
In Kochikame, Komachi Ono's parents mistakenly believe that their daughter and Kankichi Ryotsu are a couple, despite her constantly trying to tell them otherwise. They also take the two's constant bickering and fighting as their cover for flirting.
Kiyoh: Yoko! When did you have children? Don't tell me you and Kamina-?! Yoko: As if that'd happen!
In Rave Master, Haru and Elie do this a lot, starting when Haru's father asks if they are together. They finally admit their feelings near the end of the story.
Gale Glory: Ha ha! You got yourself quite a catch there, son. Nice rack too. Haru Glory: I told you... it's not like that.
Tomoe and Nanami do this a lot in Kamisama Kiss. Though by chapter 38 of the manga Nanami privately admits to herself that she hopes to change that.
In Detective Conan, Ran gets very flustered when her friend teases her about being Shinichi's girlfriend. Interestingly, this is averted at two points in the manga. The first is when Conan teasingly asks her if Shinichi is the guy she's interested in only to be surprised when she freely admits that he is. The second is during a later case, when a woman asks Ran if she has a sweetheart (or, depending on you translate it, a lover), to which Ran replies, "I do have a person I like! [...] He's really smart and he's good at soccer. He's ready to help at any time. He's really cool... He's even a better detective than Dad!"
In Attack on Titan, Ian at one point refers to Eren as Mikasa's boyfriend. She blushes and denies it.
Kyouhei and ocassionaly Sunako from The Wallflower say this when other characters infer that they have a romantic relationship. The belligerant sexual tension between the two and the quite obvious fact that the two are the hero and heroine in a romantic comedy don't help matters.
A running gag involving Steve Rogers and Sharon Carter during the Mark Waid run on Captain America. Played with in that they used to date and have a very strained relationship at present.
Peanuts: Linus is constantly telling Sally, "I'm not your sweet babboo!" In this case, HE means it, but SHE doesn't.
The phrase became so popular that there’s even a strip compilation book entitled I’m Not Your Sweet Babboo!
Y: The Last Man: Yorick frequently has to inform people that his bodyguard Agent 355 is not his girlfriend. Ironically 355 often pretends Yorick is her transsexual girlfriend in order to hide that he's the last man on Earth.
Fakir claims this about Ahiru in a Princess Tutu Abridged episode.
In Assumptions: The first sentence out of Rainbow Dash's mouth when Caramel introduces her to his siblings is clarifying that they aren't an item. His family exchanges bemused expressions, but they drop it when they decide to let the two figure it out on their own.
In Reconciliation, a Katawa Shoujo fanfic that takes place after Hanako's bad ending, Hanako says this about Sho, her publicist and the closest thing she has to a friend as of the start of the fic. They eventually become a couple.
Light: Hello, everyone, I'm Light, L's boyfr- L: My co-worker!
In the Courage the Cowardly Dog fanfic All Things End, Computer teases Courage about a dog he met in which he responds with this. He gets his revenge on Computer when Nina comes into the picture, playing up the same thing.
When Heimdall implies that Ayra is tied romantically to Nico in the Percy Jackson and the Olympians fanfic Aska, Nico answers like this for her, while laughing at the ridiculous idea.
When Kira first gets a crush on Kid in the Soul Eater fanfic Black And Gold, he immediately lets her down easy by informing her he's engaged (something L.J. avoided doing until the last minute). L.J. then claims she wouldn't care if Kira did pursue a relationship with Kid, citing the trope name.
Averted in Bravely Tangled Up With Dragons—Flynn asks Hiccup where his girlfriend went, referring to Merida, but Hiccup narrowly avoids saying this as Flynn took a tree branch to the face, swung by none other than Merida.
Played as straight as possible in the third chapter of the Full Metal Panic!AU fic Brothers in Arms, when Tessa very vocally denies that she has feelings for Garon. That stance lasts about two minutes.
In the Pokémon fanfic Cindys Story, during their Cyndaquil and Quilava years, this was the case with Cindy and Ty. In their Typhlosion forms, they are basically...er... Happily Married?
Subverted when a dream-interpreting fortuneteller assumes Adam is Kira's boyfriend (mostly because Kira was sitting on Adam's lap at the time). Since they aren't even remotely a couple (dating other people, vast age difference, barely know each other), they're rather confused by the assumption.
Akio: MOM! Miho-chan's not my girlfriend... she's my sensha-do team's captain.
A subtler example happens after Akio ends up taking care of Miho while she's recovering from her injury in the match with Anzio, Senmonka comes to see him, and asks him what he and Miho did together. Akio says that he and Miho "spent some time working on some organizational stuff for the team," which is only part of what they did. Senmonka then decides to ask if they did anything else, making Akio want to hit him, but Akio inwardly concedes that the entire arrangement isn't so bad.
Similarly, Tsubasa points out that Miho must be keeping Akio busy, but Akio points out that because of Miho's aforementioned injury, she has needed a lot of help. He then gets Tsubasa back by pointing out his relationship with Kazukonote AKA Hoshino, of Leopon Team, which Tsubasa can't deny.
The Star Trek fanfic Written in the Stars revolves around this trope for the first part of the story. Fem!Kirk discovers from Spock Prime that he and her own Prime counterpart were married...and then the spirit of that counterpart gets stuck inside her head, and makes hints about the alternate two's relationship whenever she gets the chance.
In A Far Green Country, chapter 12, when Surad mentions "your girlfriend", Elden says, "She's not my girlfriend." Surad still believes that Nellas is his girlfriend.
Treasure Planet: Doppler reacts this way when BEN thinks him and Amelia are a couple because he's carrying her. It's said with less denial and more tenderness than usually found in other examples, but that's because the film is hinting at their growing fondness for each other.
BEN: Awww, isn't that sweet? I find old-fashioned romance so touching, don't you? How about drinks for the happy couple?
Doppler: Ooo, uh- No. Thank you. We don't drink, and, uh- and, uh, we're not a couple.
In the Frozen song "Fixer Upper," Kristoff's "family" of trolls immediately assume that Anna is Kristoff's girlfriend when they meet her (after all, she's the first girl he's ever "brought home") and continue blatantly shipping them in song. Though they do falter a bit at hearing Anna is engaged to Hans, they quickly get over it and even try to marry Anna and Kristoff on the spot anyway. They actually manage to get to the vows part before the accidental participants stop them.
Kristoff: ENOUGH! She is engaged to someone else, okay?!
In Piranha 3D, Jake constantly denies that Kelly is his girlfriend, and the awkwardness is ramped up because he's on a yacht surrounded by beautiful porn stars. Kelly agrees to do a bodyshot off one of these porn stars just to rile Jake up a little.
Like Brother and Sister example when Harry says this about Hermione to a worried Viktor Krum in The Goblet of Fire and has to keep on telling that to half of Hogwarts because of Rita Skeeter's meddling. Poor Hermione is even attacked by Harry's rabid fangirls and has Molly giving her the cold shoulder for a while.
In Deathly Hallows, Harry even has to say this to Ron at one point.
In On the Jellicoe Road, Taylor denies being Jonah Griggs' girlfriend even though she is secretly in love with him (and they get together at the end anyway).
The War Against the Chtorr. In "A Matter for Men" McCarthy's Jerk Ass co-worker Ted deliberately lets an annoying officer think they're gay lovers to piss him off. McCarthy spends the rest of the novel denying that he and Ted are boyfriends, "or any other kind of friends."
Also, in the same book, Mara reveals to Luke that she wasn't "involved" with Lando.
There's a quasi-example in Death Star. Uli, a jaded surgeon who still pines after Bariss Offee, a Jedi Knight who was killed twenty years ago, is summoned to tend to Leia after she is tortured. While talking to her, as she plants the idea that he should risk imprisonment and leave Imperial service, he's struck by her eyes - they're brown. Bariss's were blue. Talking to her even for that little space of time shakes him up, and he tells his companions about her. Later this leads to them referring to her as his girlfriend, and he delivers the Stock Phrase.
In book two of Codex Alera features a simultaneous "S/he is not my mate!" from Tavi and Kitai.
In Gregor and the Marks of Secret, Gregor and Luxa are going to investigate the Nibbler's situation, but since no one can know about it, they pretend that they are going on a picnic. Or course, Howard shows up and offers to join them, so Gregor, looking for an excuse, tells him that they're going on a date. Even when Howard finds out that Gregor was lying, he still chews him out because seeing as Luxa's a princess and Gregor's not even an Underlander, they couldn't possibly be married. Gregor states several times that he and Luxa aren't like that and marriage is thinking way too far ahead, but then Howard asks Gregor why he thought Howard might believe it in the first place, rendering all his arguments useless.
Throughout most of Eclipse, Bella tries to convince everyone that Jacob is Not Her Boyfriend. Then she realizes that she does love him, but she loves Edward MORE, thus casting Jacob in the role of Unlucky Childhood Friend.
Pops up several times in The Dresden Files between Harry and different characters. (Harry isn't good with relationships.) His mysterious ex Elaine and police officer friend Murphy have each mistaken the other for his current girlfriend. Also, people mistook Harry for being in a relationship with Susan Rodriguez before he actually would go so far as to call it that, since he's the chivalrous type.
Later in the series, used between Harry and Thomas Raith. Thomas is intentionally acting flamboyantly gay. Harry is very open with and trusting of Thomas even though Thomas is a vampire, but he can't tell anyone the real reason: they're half-brothers. Not knowing the real reason, most people jump to the conclusion that Thomas is Harry's lover. At one point Harry deliberately plays that role, and some minor characters continue to give him a hard time about it.
Even later, after Molly becomes a main character, Harry also gets this with her. It doesn't help that she's his apprentice in magic, and it's something of a social norm for wizards to sleep with their apprentices.
Averted in the Darkest Powers series. Multiple times, people talking to Derek will refer to Chloe as "your girlfriend", and while talking to Chloe will refer to Derek as "your boyfriend". They never deny it. For one thing, it's not worth it- the people taunting them about it are either bad guys looking to kill and rape them, or Jerk Asshumans mocking who they think is a schizophrenic girl. For another, Chloe quickly learns that denying a relationship between them only serves to convince people she's hiding something.
Played with and lampshaded in Ryk E. Spoor and Eric Flint's novel, Boundary. A.J. and Jackie are two scientists who work together and are friends; they also bicker a lot. As such, Jackie always gets ribbed by the other people in their team about her "boyfriend" A.J. She vehemently denies these accusations to the knowing reaction of the others. Of course, when A.J. ends up with his real love interest — another scientist named Helen, which was teased earlier in the novel — Jackie smugly declares to everyone within hearing distance, "I told you he wasn't my boyfriend."
In Percy Jackson and The Battle of the Labyrinth, Percy makes it clear to his mother that his planned afternoon at the movies with Annabeth is not a date. Sally Jackson is unconvinced. One gets the distinct impression that neither is Percy. And yes, he and Annabeth do become a couple.
In Firestar, Ned DuBois is so deeply estranged from his wife, Betsy, that neither of them gives a damn anymore. Which is why he spends every third page thinking about exactly how little she must give a shit that he's disappeared to Brazil, is sleeping with every woman who will let him, and hasn't yet finished his letter to her.
In the first book of Terry Goodkind's Sword of Truth series, Zedd is introduced to Kahlan by Richard... but not before Zedd calls out Richard for being rude by not introducing him to his "girlfriend." Richard calmly denies this, only for Zedd to joke about Richard, therefore, denying that Kahlan is a girl.
In Ravenscliff, Cecile inverts it saying "He's not my brother", meaning to her cheerleader friend she has an option on her new stepbrother.
In L Jagi Lamplighter's The Unexpected Enlightenment of Rachel Griffin, Rachel about Gaius — with more than usual excuse, since they had only met a day before, and she's thinking that at their ages, their age gap is too much. Later, knowing him to be in danger, Rachel is upset because she hasn't really had a chance to consider whether she wants him as her boyfriend.
In Roger Zelazny's Lord of Light, Rudra declares that he never was romantically involved with Kali. The reason why he started hunting jackbirds after one of her lovers was incarnated as one was that he disliked their songs.
Brief example happens in the Star Trek: The Next Generation episode inheritance, where Data tells his "mother" Juliana (the wife of his creator Dr. Soong, she claims) that he's going to see Counselor Troi; Juliana assumes the two are close, and comments that she's glad that the accessories her husband designed that made him "compatible" with humans actually work. (Not a true example of the Trope, of course, because Troi is not Data's girlfriend; he was going to see her because she's the Counselor and Juliana misunderstood.)
On M*A*S*H, Colonel Potter has just become the unit commander and is getting up to speed on his staff. He calls a name, the person says "Here" (or the like), and then he reviews their record and makes some comments. He goes over Margaret Houlihan's record, compliments her, and then moves on:
Colonel Potter: Major Frank Burns. Houlihan:Just Friends, sir. (realizes) I mean, he's not here, sir.
One of the running gags of the early years of Mash was Frank and Margaret trying to hide their relationship, even though everyone in camp knew they were an item.
Happened a few times to the Doctor and Rose in the first two seasons of the 2005 revival of Doctor Who, apparently just because the writers were running out of ways to broadcast that the new show had romantic subtext.
Subverted with the Doctor and Donna Noble, who seem to do this bit about once an episode. But Donna is something of a Not Love Interest because when they say it, it really is 100% true. It's entirely without the romantic tension.
After River Song thoroughly distracts the Doctor in "The Impossible Astronaut":
Canton Delaware: So what's going on here?
The Doctor: Ah...nothing; she's just a friend.
Rory: I think he's talking about the possible alien incursion?
In a flashback scene in "Let's Kill Hitler", it's learned that Rory and Amy had denied any romantic involvement, only while Rory insisted that he and Amy were just friends, Amy at the same time said, "He's gay." She suspected his sexual preference because he had never shown the slightest interest in any girls...only to realize that he was interested in one girl. Her.
Parodied in Spaced, when Tim reacts indignantly in this fashion to a (sarcastic) suggestion from Daisy that his "boyfriend" Mike is on the phone for him... only to purr "Hi, babe." in a seductive tone as soon as he picks up the phone.
The DVD commentary puts this down to them forgetting they'd already done the joke in Spaced, Shaun's pained expression after saying it being Simon remembering during filming.
Monk: Natalie is highly amused whenever someone thinks she suppresses romantic feelings for Monk.
In "Mr. Monk and the Game Show", Monk goes on Roddy Lankman's show Treasure Chest. Before they begin the first round, Lankman asks Monk if there's anyone at home that he wants to say hello to. He mentions Sharona, causing Lankman to ask, "And how long have you and Sharona been married?" Monk quickly corrects him.
Inverted in "Mr. Monk Gets Married", where to rescue Randy's mother Maria from gold-digging antiques dealer Dalton Padron, Monk and Sharona must infiltrate a marriage counselling camp by (of course) pretending to be a couple with severely exaggerated problems, with Monk playing a cowardly mop salesman and Sharona pretending to be his alcoholic wife. Their marriage is the absolute worst one in history. When at the end they reveal the ruse, the marriage counselor is relieved.
In "Mr. Monk and the Class Reunion", Dianne Brooks finds Monk in line while people are turning in their registration forms. She asks him if he's dating, and he firmly replies no. When this happens, Monk is by himself as Natalie is heading back to her car. Later, though, Natalie has reconsidered and decides to stay with Monk for the remainder of the reunion. Naturally, when Dianne spots Monk and Natalie together at the cafeteria, this happens:
Dianne Brooks: Adrian! There you are. We've been looking for you. [Dianne notices Natalie]
Dianne Brooks: Ahh... Oh, so you two aren't... [she points between Monk and Natalie; Natalie laughs]
Natalie Teeger:[grins] No!
Also happens in one scene in "Mr. Monk Gets Lotto Fever," where Natalie is signing autographs, Monk comes up to grab some wipes from her purse and one of Natalie's fans asks her if Monk is her boyfriend. Natalie corrects the fan.
Inverted again in "Mr. Monk is Someone Else". Panicked by unwanted romantic advances from Lola, Monk quickly blurts out that he already has a girlfriend, and her name "Natalie Teegerb" (it's French Canadian).
In the Tie-In NovelMr. Monk Goes to Hawaii, when Monk and Natalie first encounter Natalie's friend Candace, she seems to think that Natalie was exaggerating her claims about Monk's OCD compulsions, in part because she's never met Monk before and because Monk happens to be on an anti-OCD drug that he takes to control himself during flights. Due to Monk not acting like himself, Candace assumes that he's her boyfriend.
Robin and Barney also spend the season five premiere firmly denying that they are boyfriend and girlfriend. They seem to have no problem admitting that they are a couple, so long as the terms "boyfriend" and "girlfriend" aren't used.
The X-Files: If it happened once, it happened a thousand times to Mulder and Scully, most notably in "The Rain King". Basically guaranteed to happen starting about mid-season four onward.
It even happens in the 2008 movie, though in reference to being married.
Father Joe: No. I can see you're a woman of faith, but not in the same things as your husband. Scully: He's not my husband.
In That '70s Show, when Jackie and Hyde started their relationship, they wouldn't admit that they're together, even though they were making out all the time.
Jackie: He is not my boyfriend. Hyde: I'm not her boyfriend. They just don't get it. Jackie: No. Why would they? Let's go, baby.
The West Wing: Josh denies a relationship between himself and Donna at least twice, once to Amy Gardner (who becomes his girlfriend after it's cleared up), and once to Lt. Commander Jack Reese (who dates Donna after confirming he's not getting in the way).
Inverted with some irony on the campaign trail in the last season.
Josh:(into the phone) No, I don't have Donna!
She's lying next to him at the time...
In the 1990's Australian series Police Rescue the two main characters, Micky and Georgia, are going to interview a witness, who asks Micky: "Is this your girlfriend?" Micky responds truthfully that no, she's his (police) partner. He later gets snarked over this by Georgia, as while it's technically true, there's always been an obvious vibe between them.
iCarly: In "iGo to Japan", the check-in clerk at a hotel mistakes the 15-year-old pair for a honeymoon couple. Freddie gives Carly an eyebrow raise and gets slapped across the face for his stupidity. In "iLike Jake", Carly gives Freddie a kiss on the nose for helping her to fix Jake's terrible singing voice, and Jake mistakes their kiss for them being together.
In the Royal Pains episode "Am I Blue?", Evan's new just-friend is under the persistent impression that Divya is his girlfriend:
Evan: Uh, we're not really... Anna: You'll make up! You're so good together.
Glory:(about Spike) He wakes up; tell your boyfriend to watch his mouth. Buffy: He is NOT my boyfriend.
In fact, Buffy often denies Spike being her boyfriend, even when it is revealed that she had slept with him.
Buffy: [Anya did] something very stupid. Xander: With your boyfriend. Buffy: He is not my boyfriend.
Technically, it was true in both those cases, as they weren't having a relationship in season 5, and in the second example, she had already broken up with him. But Buffy denied it even while they were having an ongoing sexual relationship (granted, in this scene it was partly because she was being evaluated by a social worker and he wasn't the most presentable boyfriend):
Ms. Kroger: Um, Miss Summers, if you and your boyfriend would like to— Buffy: He is NOT— (Spike looks over with a scowl; Buffy clears throat) ... not my, my boyfriend, he's, um, just... a... (Spike waits to hear what she'll say) Spike ... this nice woman is, uh, (meaningfully) from Social Services?
Buffy even denies it to Spike when they're alone together; in fact his referring to her as "love" or "my girl" is a guaranteed Berserk Button as Buffy refuses to admit they are (or should be) having anything more than comfort sex. A notable use of this trope as it's not Played for Laughs but is a sign of their Destructive Romance. In the final episode of the series, Buffy gives the most truthful version of this trope when she says that Spike isn't her boyfriend, but "he is in my heart."
The first time Buffy used this line on the show, however, it was about Angel - in season 3 episode "Revelations", when Buffy's friends finally learned that Angel was back from hell.
Buffy: What are you guys talking about? Oz: Oddly enough, your boyfriend - again. Buffy: He's not my boyfriend. Really, truly, he's... I don't know.
Then we have the comics where Buffy learns Satsu is in love with her, and they sleep together. Willow finds out and when the topic is brought up Buffy denies that Satsu is her girlfriend, before they sleep together again.
Andromeda: This happens to Dylan and Rommie at least once in the first season.
And a very good thing, too, as we see later in the season what happens when an AI avatar gets too close to her captain.
Castle has a variant; someone questioning whether Castle and Beckett are, you know, will get approximately this response:
Happened on two related episodes of Law & Order: Criminal Intent. Bobby Goren's brother Frank assumes that Alex Eames, his police partner, is Bobby's girlfriend; Bobby corrects him, but it doesn't seem to sink in (possibly because Frank is a drug user). In the next episode, Bobby gets a phone call from his hospitalized mother Frances, who says that Frank told her Bobby has a girlfriend and she wants to meet the woman. Bobby tries to explain that she's not his girlfriend but his mother hangs up on him, leaving him embarrassedly telling Alex, "My mother wants to meet you."
A variation on The Mighty Boosh. Lance Dior accuses Howard of being Vince's wife. Howard bursts out with "I'm not his wife am I! I don't know where he is at all times!" Since Everyone Can See It, Lance is Not convinced.
Usually averted. Vince is mistaken for Howard's wife/girlfriend in many episodes, and instead of denying it - like you would expect two supposedly straight male friends to do - they just look slightly pained. Seemingly it happens so often they just gave up trying to protest.
American Dreams has a couple examples with these mostly with Sam and Meg who can't get together due to Sam being black and it being 1966. JJ also gets this with a couple of his wartime romantic interests where he actually has no real interest in the girl because of Beth his fiancee back home. There was also a variation on this when one of the members of JJ's platoon is involved with a reporter, while he says this its implied they actually are he's just not telling, of course Everyone Can See It anyway.
In the season 4 premier of The Big Bang Theory, Sheldon insists that the girl he met on a dating site who has been texting with him for four months and intends to bear his children is not his girlfriend.
Sheldon: Amy Farrah Fowler has asked me to meet her mother.
Leonard: Yeah. So?
Sheldon: What does that mean?
Leonard: Well, you know how you’re always saying that Amy is a girl who’s your friend, and not your girlfriend?
Leonard: You can’t say that anymore.
They finally make a Relationship Upgrade in season 5 when Sheldon gets jealous of Amy dating other guys and ends up asking her to be his girlfriend.
The first season had this exchange:
Mrs Cooper: (To Leonard and Penny) Might say you two make a cute couple.
Penny: We're not a couple.
Leonard: Us pshh no. We're just two singles. Like the cheese...individually wrapped. Not together.
Mrs Cooper: I strike a nerve?
Howard: Oh yeah.
(of course in this case it wasn't so much denial as it was trying to cover up his painfully obvious crush).
In season five of Dexter, everyone who meets Lumen assumes that she is Dexter's girlfriend, but he insists that she is merely his "tenant". Though in fairness, she really wasn't his girlfriend at the time.
Comes up nearly every episode on Burn Notice. Everyone except Michael knows that Fiona is, in fact, his girlfriend. Michael, for his part, is only tempted by ONE other woman over the course of the series, and she turned out to be an assassin deliberately playing on every weakness he had.
Bret and Jemaine from Flight of the Conchords are sometimes mistaken for a couple, specifically by Brahbrah, a woman they were both trying to impress. It was a fair assumption to make, given that they're two thirty-something guys who share a bedroom, and they spent quite a bit of the episode wrestling each other.
Inspector Lynley and his partner Sergeant Havers. His own wife half-seriously suspects him of having an affair with her! And she's not the only one. They're not together... yet.
The song by Michael Jackson, "Billie Jean", is focused on this trope. But, it was implied that while Billie Jean was not his lover, her son was indeed his son.
Mitch Hedberg: "I don't have a girlfriend, I just know a girl who would get really angry if she heard me say that."
In The Pajama Game, Babe, in denial that she's attracted to Sid, sings "I'm Not At All In Love," a claim which is met with smirking derision from the girls:
It's easy to see that her daffy grin Is the grin she always wears, And she's breathless because She ran up a flight of stairs! Obviously! Naturally! Certainly!
Many examples in musical theatre of people singing you are not my boyfriend/girlfriend. Of course, whether they mean it or not, they'll certainly be in love with that person by the end of the show (sometimes the end of the song) :
"Make Believe" from Show Boat ("might as well make believe I love you... for to tell the truth, I do!").
Roger and Mimi in RENT. In the song "Happy New Year", Benny sings "Does your boyfriend know who your last boyfriend was?' and Roger responds "I'm not her boyfriend!".
In Pokémon Heart Gold/Soul Silver, the grandmother of the opposite gender friend of the player character (can be either gender) suggests that the characters are boyfriend and girlfriend, and one of the characters immediately denies it.
Inverted and then, well, blown up by Squall for otherwise uncharacteristic hilarity in Final Fantasy VIII. Squall is more or less forced into showing Rinoa around Balamb Garden, and stops in at Dr. Kadowaki's office. The following exchange occurs:
Kadowaki: Hi there, Squall! Oh my... it's not every day I see you walk around with a girl! Is she your girlfriend? Squall: Yes. Rinoa: Are you serious?! Squall?! I'm gonna take it seriously. Squall: I'm serious. Rinoa: Woo. I'm speechless. Squall: I'm seriously joking.
Raz: I don't know if she's really my girlfriend. I mean, I think she... Lungfish Resistance Member: I only meant she was your friend who is a girl, Goggalor.
In Beyond Good & Evil, when Jade first brings her new sidekick Double H home with her to the lighthouse, several of the orphans naturally assume he's her new boyfriend. Jade quickly tries to correct them.
Jade: I swear, he's not like the others!
In Tales of the Abyss, there is one point where the party returns to the first real dungeon the game had. Luke and Tear, having been the only party members at that point, remark upon how it was night when they were last here, which leads to the rest of the party wondering why on earth they didn't know that Luke and Tear were "in a place like this, alone, at night." Luke quickly exclaims "It wasn't like that!" and starts hastily trying to explain himself when Tear suddenly states simply, "The very idea is absurd." Luke is visibly stung, indicating that perhaps he falls under the third example at the top. Of course, any sympathy the player may feel for Luke is immediately replaced by laughter over Jade'sbrilliant reaction to the whole thing.
Tear: The very idea is absurd. (walks away a bit, everyone else remains in place) What are you doing? Come on. Luke: ...Now I'm mad. Guy: Damn, that was cold... Jade:(sounding VERY happy) Yes, it was. Guy: You sound like you're having fun, Colonel. Jade: More than you could ever imagine. Guy: ...You're horrible.
It happens a lot between the two. The second OVA has this frequently.
In Tales of Rebirth, Tytree at one point refers to Claire as "Veigue's girlfriend", to which he calmly responds "She's just a childhood friend". It would be an inversion to the usual reaction a character is supposed to have, but then again, he's Veigue...
In Hyperdimension Neptunia in the second game, Mk2, IF snaps when the rest of the cast is saying that they would like to have Compa as a wife, so she claims she belongs to her, immediately realizing what she just said and claiming that she didn't mean it like that. Something similar happens in the trailer of the videogame Geki Noire, with Noire talking without thinking about Neptune.
In Castlevania, in both Sorrow games, Soma frequently feels the need to point out that Mina is not his girlfriend, despite the fact that its obvious to everyone else that she's his designated Love Interest. He will actually become Dracula if he sees his beau hurt, but she's n-n-not his girlfriend.
This is actually said completely seriously in Portrait of Ruin. Whether or not Jonathan and Charlotte are still in the denial stage and/or just have really good poker faces is up to you:
Vincent: Even so... the two brave vampire hunters! I envy you! or Vincent:(sigh) The perfect couple! I'm slightly jealous! or Vincent: Hi there... the young couple! So naive! Jonathan: She's like my kid sister! Charlotte:Jonathan!Stop treating me like a child!
Odd example: Mortal Kombat: Shaolin Monks. Kung Lao takes a jab at Liu Kang whenever Kitana is seen or mentioned with the former denying any relationship. In canon, it's heavily implied they are supposed to be just that.
Given a nod in the latest game, during Kung Lao's story mode chapter wherein he and Liu Kang search for Kitana:
Kung Lao: I hope your girlfriend is worth Lord Raiden's anger, Liu Kang.
Liu Kang: Notice that I am ignoring you.
There are examples of this trope in Baldur's Gate 2. Jaheira does it at least twice (once in an incident involving a magical locket, another when you are awakened by bandits).
Implied usage in Half-Life 2: Episode 2. A random resistance member asks Alyx "So, is he your boyfriend or something?" in regards to Gordon. Gordon himself is out of earshot before her answer is heard.
However, she doesn't really object when her own father hints at it being quite obvious. And she seems much more embarrassed about her father talking about such things, then about what he said.
Rozalin: Adell! This is not the time to mention that!
In Sam and Max Episode 201, Sybil and Abe Lincoln were not dating... up until Max begins insisting that the meeting is something absolutely crazy.
Played with in Devil Survivor. When first speaking to Gin, he asks who the player is. The player can either say their name or "Yuzu's boyfriend". If the player chooses the "other" option, Yuzu gets very shocked.
She has a similar reaction later, when Atsuro jokes that Haru might be her competition for the protagonist's affections.
The same thing happens to Yuzu's Devil Survivor 2 counterpart, Io. During a Fate Event in which Io is trying to talk a boy out of suicide, the player can choose to introduce himself as her boyfriend. She of course denies it but, being a fairly bashful character, is more flustered than anything and decides to take it as a joke, as the player character apparently likes to joke a lot.
Makes an appearance in Persona 3 Portable when playing as a female main character. If attending the Summer Festival with Akihiko, a takoyaki vendor will ask if she is his girlfriend, prompting him to stutter an angry denial. It's as if the idea had crossed his mind before... This also happens frequently with femele protagonist and Junpei.
This is invoked in Fire Emblem: Radiant Dawn when Ike asks Haar why Jill isn't with him. Haar denies anything beyond friendship towards Jill. Two chapters after this base conversation, Haar can recruit Jill into the Greil Mercenaries. Of course, if Haar and Jill get an A-Rank support formed, the ending will imply a marriage between the two without actually saying anything specific.
Haar: She is simply the daughter of my dead teacher. Nothing more.
Ar Tonelico 2. Cloche would like you to know that Croix is her dog and bodyguard, NOTHING ELSE! The fact that she goes on dates with him is completely irrelevant.
Makes an appearance in Dragon Age: Origins Witch Hunt when Ariane enquires about the exact relationship between a Male Warden and Morrigan. Apparently when they think no-one is looking, the Warden often absent-mindedly plays with the ring Morrigan gave them, causing Ariane to wonder if her knowledge of the significance of humans sharing rings is accurate.
During the later ranks of her social link, Yukiko tells the Protagonist that they have been spending so much time together that the staff at her family's inn assumes that he is her boyfriend. She denies it, of course, but by then it's pretty clear that she really wants to be proven wrong, the sooner the better.
Chie and Yosuke. Kanji at first assumes they are a couple, much to Chie's annoyance. Speaking of Chie, if she's your romantic partner and date to the Summer Festival, she has this as a knee jerk reaction to a vendor calling him her boyfriend, only to realize that it is, in fact, true.
Played with in the second and third games between Maya Fey and Phoenix Wright. Pearl assumes the two are a couple, and it seems no amount of red-faced protests will dissuade her.
In the Phoenix Wright manga collection, Pearl asks Phoenix about his relationship with Maya, and is met with five Psyche-locks, which within the games, signify a secret that is as well-guarded as possible.
Gumshoe pretty much outright uses this line for defense, as well, with regards to Maggey Byrde. Phoenix doesn't buy it for a moment.
Phoenix: (Note to self: Gossip with Maya about this later!)
In Ace Attorney Investigations 2, Tateyuki asks if Kay is Edgeworth's girlfriend after he gives up his badge to continue defending her from murder charges. Edgeworth responds that she is his assistant and that he is responsible for her.
Apollo has this reaction in Dual Destinies when Klavier assumes Athena is his girlfriend.
Everyone seems to be under the impression that Toko and Reiji have some kind of relationship in Kara no Shoujo. Rather than being defensive about it, Reiji is mostly bemused.
Yamato in Maji De Watashi Ni Koi Shinasai, regarding Miyako, all the time - though he's actually got a reason to do so. Except, of course, in her path, where he comes around rather quickly once he's made his decision. There are also choices in the game where, if you actually say she is your girlfriend, you'll immediately end up in an ending with her, whether you were joking or not.
Rin Tohsaka in Fate/stay night can get like this. Especially prevalent in one scene in "Unlimited Blade Works", where Shirou can warn Lancer to stay away from Tohsaka, to which she keeps desperately denying that she and Shirou are in love, while Shirou just smirks and doesn't deny anything, and Lancer laughs his ass off at Rin's reaction.
Rin: Why are you not saying anything? This is looking as if we actually are in love!
Lancer: (laughing) Please. There's no "as if" about it!
In Higurashi Daybreak, the Higurashi: When They Cry fighting game, when you're playing Story Mode as a Keiichi-Rena team, most of the adults will ask if you're a couple. Rena is delighted at the notion, but Keiichi protests. This actually becomes the stakes for the last two battles, thanks to a Love Triangle with Mion at her most Tsundere.
Played with in Friendly Hostility: Fox normally has no problem in referring to Collin as his boyfriend, but when Collin shows up while his coworker Derringer is pestering him about becoming buddies, he quickly rushes to loudly introduce him to Derringer as his "BEST FRIEND". Collin just as quickly walks off before he gets mad enough to do something he'll regret.
Issac and Joy in Namir Deiter, though it's only by mutual agreement (and a boatload of issues) that they're not.
Except they've recently been upgraded to Beta/Tertiary couple, after an argument while on a double-date (with different people).
Shadehawk and Crossroad in Antihero for Hire, though with all the UST between them, some feel it's only a matter of time. The most notable example is here:
Hector: Looks like your girlfriend's coming to the party. Shadehawk: Ugh. You are such a depraved monster. Insinuating that she's my girlfriend, I mean.
In The Inexplicable Adventures of Bob!, Bob frequently has to reiterate to his girlfriend Jean that there is nothing between him and the alien Princess Voluptua. Despite the fact that they have kissed. And that Voluptua is now stationed in Earth's solar system. And that she is a Stripperiffically-cladHello, Nurse! of the first order. Because Bob knows that she is in fact, under her disguise, a giant alien bug.
Boris, the robotic spider in Bugs, has shouted more than once that a real spider with a keen interest in him is not his girlfriend.
However, in the short term at least, this turns out to be true. Jack has a crush on Zimmy of all people, and Annie, at the time of making the aforementioned statement, held a hidden grudge against Jack. They're likely in for more teasing of that sort now, though, considering that as far as their classmates are concerned Jack publicly gave Annie a note and some of them saw them amiably chatting then going off on their own for a night. Of course, there's a nonromantic explanation for those, but others don't know that.
Dwayne: That was quite an adventure you guys had. How's Dexter? Patty: Argh! Not you too! Look, we are not dating! We made peace! That's it! Not seeing each other, not dating, not engaged, not getting married, not breeding! "Friends" is pushing the definition! We just aren't fighting anymore!
Several people in Questionable Content refer to Angus as Faye's boyfriend or something similar before they are officially an item, but have admitted their mutual attraction. Faye denies this.
In Ears for Elves, Donny sees Tanna walking arm-in-arm with Rolan. Donny infers that Rolan must be her boyfriend, and finds this disgusting; Tanna protests madly. A while later, Donny tells Tanna that her new boyfriend isn't so bad after all; her reaction is to say that Rolan is not her boyfriend.
In one story arc for Cheer!, Lita forces Alex (who is a girl, yes) to take her out to dinner to a steak house. She also forces Alex to go to the dinner wearing a nice suit. Cue Alex spending most of the evening telling the restaurant staff that she is not Lita's date and not a "sir".
In Footloose, Jenny refers to Keti as Dan's girlfriend - she, Dan, and Iordan insist she isn't in unison, Keti and Dan being genuinely Squicked by the idea, and Iordan having a vested interest in Keti being single.
In Homestuck, Terezi seems to inspire a lot of this. Karkat repeatedly denies having a "thing" with her when numerous other characters notice their bond, and Dave denies dating her when Karkat starts getting jealous.
As far as Lisa and Ally of Sunstone are concerned; she is just the woman I live with, have lots of kinky sexy with, and spend most of my time with. This delusion is upheld by the characters so they don't have to question weather they are homoromantic or if the other reciprocates; but all their closer friends can see through it.
In The Guild, Codex insists that "there is no circumstance under which [she and Zaboo] are together in any shape or form". Zaboo feels differently.
Simon from Shadow Of The Templar takes this to new heights when he tells Jeremy that he's not even his friend despite them being familiar with each other in the horizontal position. He does answer "maybe" instead of denying the possibility outright when the criminal who kidnapped Jeremy asks him if he's his boyfriend, but goes right back to denying it soon after.Then when he finally overcomes enough (but not all) of his Selective Obliviousness and Tsundere issues to call Jeremy a friend, Sandra scoffs and says that they're "special friends" at the very least, to his chagrin.
In "Thanks For The Feedback: Date With Doug", The Nostalgia Chick denies having any attraction to The Nostalgia Critic. It was a little too firm to be believed anyway, but lost all credibility when Doug and Lindsay confirmed later that the characters already had sex at this point.
She does it again (just with the word "ally" instead of "boyfriend") when Mara Wilson wants to kill her to hurt him, but contradicts herself a few minutes later when they both mope about missing him.
Web Serial Novel
In Statless And Tactless Joe is convinced that Soo and Ian are dating because they occasionally allude to meeting offline. Any incident involving such an event getting mentioned invariably leads to the group getting sidetracked to refute it.
Also counts as ironic Book Ends- In the beginning of the first episode, they're protesting vehemently that they do not have a relationship. At the end of the last, they finally kiss.
Teen Titans: Robin really ticks Starfire off when he says this in the episode "Stranded". Can't really hold it against him though, as thanks to her established role as The Ditz, Cloudcuckoolander, being raised by aliens, etc., he naturally assumed she didn't even know what a girlfriend was. He is sadly mistaken, as she is quick to inform him. It actually makes the current situation dangerous, as Starfire's powers depend on her emotions, and being confused makes her unable to use them; not good, seeing as they are on a planet with a hostile environment.
That and the episode "Date With Destiny". Robin invokes the trope name, but this time, against Kitten.
"Stranded" also gives us one of the best responses from someone who speaks broken English. Watch it here, starting at 1:20:
Starfire: I am not your friend? Robin: Uh... Starfire: I am not a girl?
Arthur: Francine and Arthur simultaneously fulfill this trope in an early episode.
Codename: Kids Next Door: Nigel tells his friends this about Lizzie, who actually is his girlfriend, because he's embarrassed.
Don't forget Wallabee and Kuki (Numbah Four and Numbah Three).
Numbah Two and Numbah Five: Wally and Kuki, sitting in a tree! K-I-S-S-I-N-G!
Zuko snaps "She is not my girlfriend!" at a waiter who calls a girl he was on a date with his "girlfriend", though it's not exactly an unreasonable assumption. Oddly enough, when Jun once called an archenemy his "girlfriend" a season earlier, he barely even reacted.
Although they reacted far more strongly to Jun's accusation in the finale. (Sorry, wrong show.)
Jun: I see you worked things out with your girlfriend. Zuko:(spit-takes) She's not my girlfriend! Katara:(simultaneously) I'm not his girlfriend!
Also in the second episode:
Sokka:(referring to Aang) We're going to save your boyfriend. Katara: He's not my... Sokka: Whatever.
French version of the above:
Katara: He's not my boyfriend.
Sokka: Not yet.
Also happens when Toph meets Jet for the first time (not having joined the group until after his first appearance):
Jenny: Okay... listen up, because I'm only gonna say this once: Sheldon is not my boyfriend! I don't even know him! He's just some crazy, loser, stalker geek! He's not my boyfriend, he's not my friend, he's not my anything!
And Sheldon heard the whole thing. Ouch.
It was bad enough that even the villains of the episode felt sorry for the guy.
Said by Mac in the first episode of Foster's Home for Imaginary Friends featuring Goo. This was done not only due to Mac being eight years old and embarrassed, but also because it was true, and Goo was being a real pest to everyone. Naturally, no one believes him.
Goo, who was living in her own little world at the time, probably never even suspected that anyone (let alone everyone) thought she was Mac's girlfriend.
Chowder: the episode "Chowder's Girlfriend" was devoted to Chowder trying to convince Panini that he's not her boyfriend! Since that episode, he yells that at her if she so much as says "Hi!" to him.
Oddly, most likely due to serialized series and a tendency to be aired "out of order", it's his response to her in the first aired episode as well.
Even more strangely, at the end of the series Chowder is married to her. Or so Panini would lead the audience to believe.
Tommy from Robot Boy doesn't like it when people call Lola his girlfriend.
In the Ben 10: Alien Force episode "Plumber's Helpers", when Helen calls Kevin Gwen's boyfriend, she angrily denies that is so... despite the fact that a few episodes earlier, she was complaining that Kevin wasn't asking her out.
Happens earlier in the series, too, in "What Are Little Girls Made Of?", though not as drawn-out. Gwen lets Ben and Kevin climb into her room through the window, and her father asks if he's her boyfriend. They both quickly reply "No!" and Gwen blushes.
In another episode, Ben simply asks her where Kevin is, and Gwen launches into a full-blown rant about how he isn't her boyfriend.
In Code Lyoko, Yumi and Ulrich frequently state these kinds of denial, mostly spurred by Odd's innuendos or, in Yumi's case, her brother Hiroki's hounding. Yumi also says "He's not my boyfriend" about William, but in this case it is genuine, especially once he becomes an enemy.
Yumi manages to invert, then play the trope straight, in just one line:
Yumi: Yeah? Well, it's not the same thing. I'm Ulrich's girlfriend! I mean, I'm—I'm his good friend.
An episode of The Fairly OddParents had a group of aliens mistaking Vicky for Timmy's girlfriend. Naturally, Timmy is repulsed by the idea.
Done in the first episode of season 3 in Atomic Betty. When Betty finds out her best friend Noah has been kidnapped, Sparky makes a quip about going to save her "boyfriend," which prompts her to respond with this trope. Also comes with the obligatory Ship Tease during the rescue of someone they think is Noah (but is actually a disguised infiltrator).
Sparky: "He's not her boyfriend." Yeah right! (turns to X-5) Would you kick that much booty if that were me dangling up there?
A twist in W.I.T.C.H.: Irma initially can't stand geeky Martin, but an unintentional romantic moment between them leads him to spread the word around that they're dating. Eventually Irma does develop feelings for Martin, but by then has publically humiliated him and won't actually make a move. When Big Bad Nerissa comes to school disguised as the hot new girl and casts a love spell on all the boys, Irma has to adamantly remind herself that Martin isn't her boyfriend and she has no right to get mad at him for fawning over Nerissa.
Hilariously played in a Ho Yay situation by Ren in The Ren and Stimpy Adult Party Cartoon episode "Ren Seeks Help". Ren decides to go to a psychologist and speak about his problems with controlling anger and thus his psychical and physical abuse of Stimpy. He starts with his childhood, naturally, and when he gets to the point of meeting Stimpy, he says a few words and then promptly stops.
Oddly averted in Futurama: Leela wakes up from a dream about Fry (after the latter died), to find his jacket draped over her shoulders. She triumphantly yells "He's alive! HE'S ALIVE!", prompting her neighbor to yell through the wall "Shut up! My boyfriend's alive too!" Although Leela has been rejecting Fry's advances (and in obvious denial) for over two seasons by now, at the moment she's too ecstatic to remember that he's not supposed to be her boyfriend.
Patrick had to go undercover (because he thinks someone is going to kick him out of town), so he dressed up as "Patricia". SpongeBob SquarePants had to tell a few folks "she" wasn't his GF.
The Western Animation series of Earthworm Jim is an inversion of this, where the eponymous mutated annelid insists that the Action Girl Princess Whats-Her-Name (a Cute Monster Girl who is basically an alien bug) is his girlfriend, even though nobody else around seems to think they're together. This includes the Princess herself.
Raph: *Laughing* You got beaten up... by a monkey... in front of your girlfriend!?
Donnie: She's not my girlfriend!
On Sym-Bionic Titan, Octus says these exact words to Lance and Ilana after they catch him with Kimmy. Of course, they kiss and start dating shortly afterward. Also, Lance and Ilana, who're masquerading as siblings, are asked this by their Nosy Neighbor Barb. Ilana calmly states he's her brother upon first meeting her. However, they play this trope a bit straight when Siefert refers to Ilana as Lance's "lady."
Lance: [simultaneously] We're just friends!
Ilana: [simultaneously] He's my brother!
The Secret Saturdays: A large chunk of the dialogue in "Curse of the Stolen Tiger" is devoted to Zak denying that he has a crush on Wadi.
On Franklin, this happens with the title character and Beaver's cousin Betty in "Franklin and Betty." They really are just friends, and though the ribbing causes Franklin to briefly break off the friendship, the story ends with Franklin (with some prodding from Bear) deciding that it's okay to play with Betty, regardless of what anyone else thinks. As for Beaver, she's thrilled, as she was becoming annoyed by Betty's moping. This also comes up with Samantha in Franklin and the Turtle Lake Treasure, though by the end of the film, they definitely seem to be in Puppy Love.